The invention relates to a micromechanical rate of rotation sensor in the case of which parts made of silicon, silicon compounds or silicon/glass compounds or other semiconductor materials are structured out by micromechanical techniques.
The fields of application of such rate of rotation sensors are diverse. Thus, in the field of automotive engineering, the yaw, pitch and roll velocity as the key quantity for driving dynamics control systems (ABS, ADS, ASS, ASR, and others), for navigation systems as a supplement to the GPS as well as for measuring the angular velocity of moved parts of a motor vehicle with respect to one another can be determined. In space operations, such systems can be used as weight- and space-saving inertial components (inertial platform), for stabilizing the focal plane of optical observation instruments of satellites and for measuring and stabilizing (undamped) vibrations of elastic components.
In aviation, the measuring and controlling of the relative movement of different airplane components with respect to one another (adaptive wings) can take place. A use is also possible in the case of the orbit stabilization and navigation of missiles.
In railroad technology, the yaw and roll angle of the cars with individual wheel suspensions (compare Pendolino), thus, the actual value for controlling the optimal curve entering speed can be measured.
In automation technology, robot movements can be monitored and robot components can be controlled.
In general machine construction, such components are useful for vibration measuring (compare Active Vibration Control); particularly for measuring that component of the impedance of vibrating elastic structures which originates from the xe2x80x9crotation partxe2x80x9d of the movement. The miniaturization (low weight and low space requirement) is particularly decisive here.
Finally, application possibilities exist, for example, in medical technology for monitoring patients by measuring their movements, for controlling surgical instruments (minimal invasive surgery) and for controlling wheelchairs.
The many application possibilities have already resulted in numerous suggestions with respect to rate of rotation sensors.
In the meantime, various principles for measuring the rate of rotation have also been miniaturized in order to be manufactured at reasonable cost and in order to be usable for applications in video cameras, vehicles or other moved objects. Implementations are known in metal with a piezoelectric actuator system and sensor system, as well as in quartz, in crystalline silicon and in polysilicon.
Thus, systems are described in German Patent Document DE 42 28 795 A1 (Bosch), in European Patent Document EP 05 72 976 A1 (Canon) and in Patent Document WO 93/14409 (Sunstrand) in the case of which one or several acceleration sensor(s) (BS) are mounted on vibrating structures and which measure the Coriolis acceleration occurring when the system rotates. In this case, it is disadvantageous that the rigidity of the structure on which the two sensors are situated cannot be ensured or is very difficult to ensure. In addition, the crosstalk of the excitation movement onto the sensor component cannot be eliminated, particularly if only one acceleration sensor respectively is used for each direction.
German Patent Document DE 35 09 948 A1 (Draper) and European Patent Document EP 0 422 280 A2 (Draper) describe rate of rotation sensors whose geometry is based on a miniaturized cardanic suspension (gimbal). If the overall system is rotated about a suitable axis, a rotary vibration about the suspension of the outer frame is coupled to a rotary vibration about the suspension of the inside frame (and/or vice versa). Here, it is a disadvantage that the indicated three-dimensional geometry for the optimal sensor function requires the generating of mechanically tension-free structures or structures with defined bracing, which is very difficult to implement. For achieving a sufficiently high measuring effect, a special arrangement of the inert mass on the sensor is required. This mass must be arranged symmetrically to an axis perpendicularly to the wafer plane on the cardanic structure. The technological implementation of such a construction presents serious problems; that is, the manufacturing of the sensors in the batch process with the goal of large piece numbers is very cost-intensive.
From Patent Document WO 93/05400 (BEI-Electronics), an electrostatically or electromagnetically excited rate of rotation sensor is known which consists of a disk which carries out small periodic rotating movements in the wafer plane. A rotation of the system about an axis in parallel to the wafer plane causes a tilting of the disk with respect to the movement plane. This tilting is measured by piezoresistive sensors in the four elastic suspensions of the disk. The disadvantages are that this sensor can be manufactured to be mechanically free of tensions only at high expenditures and that the tilting of the disk in a rotated system of coordinates has the effect that the controlling of the capacitive excitation of the periodic rotating movements of the disk results in high expenditures.
European Patent Document EP 0 519 404 A1 (Honda) describes a gas flow sensor according to the anemometer principle in the case of which the effect of a rate of rotation is measured by way of the change of the differential resistance of a pair of conductors. This pair of conductors is situated in the wall of a small Si tube through which gas flows and measures the change of direction of the gas flow on the basis of the Coriolis force. The disadvantages here are that the system for supplying and controlling the gas requires additional actuator systems (such as valves and/or pumps) as well as an additional periphery for the gas storage and feeding, etc. The presence of these components is a prerequisite in this patent. In addition, a very high temperature sensitivity must be expected because of the use of a gas.
The already miniaturized geometries and operating methods also include different types of tuning fork sensors for measuring the rate of rotation. They are known, for example, from European Patent Document EP 0 574 143 A1 (Lucas), Patent Document WO 93/05401 (Draper), German Patent Document DE 40 22 485 A1, Patent Document 92/01941 (Bosch) and German Patent Document DE 40 41 582 A1 (Bosch). In the case of all tuning fork sensors described therein, the prongs are excited to perform vibrations in parallel to the wafer plane. If the sensor system is entered into a rotated system of coordinates, this results in a bending of the prongs in a plane perpendicular to the excitation direction and/or a torsion of the prong suspension.
Patent Document WO 93/05401 (Draper), German Patent Document DE 40 22 485 A1, Patent Document WP 92/01941 (Bosch) and German Patent Document DE 40 41 582 A1 (Bosch) relate to twice (on both sides) suspended tuning fork sensors. It must therefore be expected that these sensors have a considerable temperature sensitivity. The electrostatic excitation of the prongs suggested in most of the embodiments as well as the read-out of the signal imply non-linearities which lead to considerable control expenditures. In the case of the embodiments of Patent Document WO 93/05401, a mechanically tension-free structuring also presents problems.
A tuning fork sensor which is suspended on one side and has a piezoresistive read-out of the torsion of the tuning fork suspension is known from European Patent Document EP 0574 143 A1 (Lucas). The tuning fork is excited electrostatically by way of an interdigital structure to perform vibrations in the wafer plane. Because of the low structural depth of the sensor element (perpendicularly to the wafer plane), the ensuring of the stiffness of the tuning fork base and of the prongs in this direction presents a problem here. However, this stiffness is required for implementing a signal read-out of the rate of rotation by way of the torsion of the tuning fork suspension.
It is an object of the invention to provide a miniaturized system which can be manufactured on a large scale at a reasonable price and which can be used for measuring the rate of rotation (angular velocity) of moved bodies in all areas of technology.
This object is achieved by providing a micromechanical rate of rotation sensor in the case of which parts made of silicon, silicon compounds or silicon/glass compounds or other semiconductor materials are structured out by micromechanical techniques, characterized in that the rate of rotation sensor has the form of a tuning fork (S) whose prongs (Z1, Z2) are situated in planes in parallel to the surface of the semiconductor wafers (OW, UW), in that these prongs (Z1, Z2) can be excited to carry out vibrations in a plane perpendicular to the wafer plane; and in that it has a sensor element (S) which measures the angular velocity of a rotation of the sensor about an axis in parallel to the tuning fork suspension.
The solution according to the invention leads to the following advantages:
The miniaturization can be advanced to a considerable degree since the solution is robust with respect to shock because of the low mass and the symmetrical construction, and saves costs, weight, space and energy.
By way of batch processes, the manufacturing method permits high piece numbers and a good reproducibility and is reasonable with respect to cost. The CMOS-compatible manufacturing also ensures the prerequisite for the monolithic integratability with the electronic sensor system or parts thereof as well as other suitable micromechanical components.
The monolithic integratability with the electronic sensor system or with parts thereof to form a robust rate of rotation sensor at reasonable cost, for example, with acceleration sensors to form micro-inertial components, is particularly advantageous.
Other special advantages of the suggested sensor geometry and of the corresponding sensor manufacturing process for the prongs in the wafer plane is the design freedom of the prongs, sufficient surface for the actuator system (such as a piezoelectric actuator system, a capacitive actuator system, etc.xe2x80x94see below), the precise manufacturing of the prong geometry in the wafer plane by using photolithographic processes, the highly accurate adjusting of the prong thickness by the utilization of buried etching stop layers while using SiliconOnInsulator material (manufactured, for example, by known BESOI or SIMOX processes) and the trimmability on the prong surface.
By the coupling to the torsion of the tuning fork suspension, the excitation movement is separated from the read-out movement.
An advantage in comparison to metal sensors and quartz sensors is the fact that the necessary hybrid-type integration of the quartz component with the electronic system does not permit a cost reduction potential of the manufacturing which is as high as that of the silicon sensors.